Fix 3DS builds

[pikhq]

I wanted to give this a shot, and I noticed the 3DS builds were broken, from two issues:

1. The devkitarm docker image was no longer able to do apt-get update. A quick bump got that working
2. steveice10 deleted their github account, along with all repos! I switched to cartene1ns' repo. They are a developer on another project (easyrpg.org) that targets the 3DS, and they appear to be lightly maintaining a fork of 3ds-bannertool. Their fork switched to using cmake, hence the remaining changes.

At least locally, those got a working build again.